Small chamber study of lead exposures from manual soldering of microelectronics

Airborne and surface Pb concentrations were measured inside a glovebox chamber with controlled inflow rate at 1.0 L/min of ultrapure air over a 4-hour period while an operator completed 1,680 solder connections using Sn63:Pb37 solder with rosin flux core. Chamber atmosphere showed released mean Pb mass of 0.0238 ± 0.011 μg and mean airborne concentration of 0.176 ± 0.085 μg/m3. Of the total solder mass used in two trials, on average 4.65% was recovered from the tip cleaning sponge and 0.14% dropped onto the work surface, with a surface loading rate of 0.30–0.45 μg/cm2. The estimated fingertip surface area in contact with solder wire was 14.7 cm2, with a measured average Pb mass of 14.9 μg, and a corresponding dermal loading rate of 1.01 μg/cm2. The waste solder dross surface area determined from digital micrographs in each trial were 1.65 and 2.43 cm2, with corresponding Pb density of 714 and 610 mg/cm2 and >90% of the detected dross mass comprising particles >100 μm in the widest dimension. Corresponding increases in blood Pb levels estimated using physiologically-based pharmacokinetic modeling were negligible compared with background. These findings demonstrate very low Pb emissions to air and surfaces during intensive manual microelectronic soldering activities.